Xinyunliang River is one of the major rivers which flow into Lake Dianchi. Water quality of the river effects the ecological health and environmental safety of Lake Dianchi. We employed single factor pollution indexes to investigate the seasonal variation of the water quality and the main factors which affect the quality. We studied the impact of the riparian ecological restoration on the river water quality taking the lower reaches of Xinyunliang River as an example. The results showed that there were obvious temporal variations in the concentration of ammonia nitrogen, total nitrogen, total phosphorus and chemical oxygen demand. All of the indicates showed declined tendency from May to November which is coincided with the rainy season, and were increased and significantly higher than those from November to next year's April, the dry season. The quality of the water is much worse than Grade Ⅴ. The removal efficiency of pollutant in timber pile banks was higher than that in vertical cement banks. The removal efficiency in summer is much higher than that in winter.